Add toSignedInteger primitive.

[brianhuffman]

No description provided.

[brianhuffman]

There is a single failing CI test; the logs include output like

> What4 exception:
> Could not parse solver response:
>   Solver response parsing failure.
> *** Exception: Parse exception: Failed reading: empty
> Attempting to parse input for get ack:
> Nothing
> 
> in response to commands for get ack:
> (set-option :print-success true)

[brianhuffman]

I'm going to assume that the CI failure is some kind of solver download/installation issue and ignore it.